1. Field of the Invention
The present invention relates to a thermocouple-type temperature-detecting device capable of quickly and repeatedly measuring a high temperature of a molten metal such as molten iron, etc.
2. Description of the Prior Art
Hitherto, as a material of a temperature-detecting device using a thermocouple for measuring molten iron of about 1500xc2x0 C., Ptxe2x80x94Rh having a relatively high melting point and being stable in the air as a thermocouple is used as the element wire and a temperature-detecting element having the structure wherein comprising the Ptxe2x80x94Rh element wire is fixed in a pipe (protective pipe) made of a quartz glass such as alumina-silica fibers, etc., has been used.
However, with such a thermocouple-type temperature-detecting device, after being used for temperature measurement of a molten metal about one or two times at steel making, the correct temperature measurement becomes impossible, therefore such temperature-detecting device is then discarded at the present condition. As the temperature-detecting device cannot be repeatedly used, many thermocouple-type temperature-detecting devices are required, that result in a high cost and inconvenience.
Also, as the material of the protective pipe of a thermocouple-type temperature-detecting device for measuring the temperature of a molten metal, a cermet, silicon nitride, alumina, silicon carbide, etc., are used to prepare the protective pipe and the temperature-detecting device having a structure in that a Ptxe2x80x94Rh wire or a Wxe2x80x94Re element wire is inserted inside of the protective pipe is known. However, because the protective pipe of such a thermocouple-type temperature detective device has a poor thermal shock resistance, it is required to carry out a treatment such as pre-heating, etc., to a temperature near the measuring temperature before measuring the temperature.
Also, in Japanese patent application Kokai publication No. 6-160200, an airtight terminal-attached sheath-type thermocouple-type temperature-detecting device is proposed. The temperature-detecting device has a function of not causing a measurement error even when a temperature gradient occurs at the terminal portion by a transient temperature change, etc., and is constituted by inserting a thermocouple element wire composed of different kinds of metal wires, an alumel wire and a chromel wire into a stainless steel-made sheath together with an inorganic insulating material, being insulated each other, and the proximal end of the sheath is air-tightly sealed by an airtight terminal portion.
The thermal shock resistance of the cermet protective pipe has a strength of 1.5 times that of the Si3N4 protective pipe, and thus when the thermocouple-type temperature-detecting device having the protective pipe made of Si3N4 is directly dipped in a molten iron of a temperature of at least 1700xc2x0 C., cracks and the like occur in the protective pipe in a relatively short time and the pipe is broken.
Also, a Ptxe2x80x94Rh thermocouple cannot be used in an inert gas atmosphere, and as the usable temperature in the air, 1500xc2x0 C. is the limiting temperature. For example, the temperature measurement of molten iron is over the upper limit of the guaranteed temperature, and a correct temperature measurement cannot be performed as well as there is a problem that a temperature to be detected is 1700xc2x0 C., a temperature near to the melting point, so that the life has to be short.
Furthermore, the thermo electromotive force of the PR thermocouple using the Ptxe2x80x94Rh element wire is small as about {fraction (1/15)} of that of a constantan.alumel (CA) thermocouple and about {fraction (1/7)} of that of the tungsten.rhenium (Wxe2x80x94Re) thermocouple, whereby there are problems that the PR thermocouple is inferior in the measurement accuracy responsiveness as compared with these thermocouples and the also inferior. Accordingly, in the measurement site, for example, in the case of measuring the temperature of the molten metal in a blast furnace, a worker must be stay at the measurement site, near the blast furnace, for from about 10 to 15 seconds until the temperature of the detective device is stabilized.
The Wxe2x80x94Re thermocouple can be used in the air and in an inert gas atmosphere, but as the usable temperature in the air, 400xc2x0 C. is the limiting temperature however, as the usable temperature in an inert gas atmosphere, 2300xc2x0 C. is the limiting temperature, that allows the measurement of a high temperature. On the other hand, the Wxe2x80x94Re element wire is liable to be oxidized in the air and there is a problem that it cannot be used for the measurement of the temperature of molten iron.
As described above, in thermocouple-type temperature-detecting device of prior art, there is a problem that in the case of dipping in a molten metal of at least 1450xc2x0 C., by the repeating thermal shock to the protective pipe, in the measurements of several times, the protective pipe is frequently cracked and is broken, whereby the temperature measurement becomes impossible.
Also, because the thermocouple-type temperature-detecting device of prior art has the structure that an alloy element wire is inserted in a protective pipe, there is a problem that air is sometimes collected at the tip portion of the protective pipe, whereby the responsiveness becomes poor and the alloy element wire is liable to be cut.
Also, the thermocouple-type temperature-detecting device of prior art has a problem that in the case of measuring the temperature of a molten metal, molten iron, slag, etc., are attached to the outer surface of the protective pipe to deteriorate the electric heating property and the responsiveness, and lower the durability thereof. Furthermore, there are problems that a molten metal attaches to the Ptxe2x80x94Rh element wire and the protective pipe of the thermocouple, the work of removing the attached molten metal becomes complicated, and also the life of the existing article is the temperature measurement of only about twice and the exchanging work of thermocouple takes a time.
The present invention has been made for solving the above-described various problems of thermocouple-type temperature-detecting devices of prior art, and an object of the invention is to provide a thermocouple-type temperature-detecting device having a good responsiveness to a temperature measurement, a strong thermal shock resistance, and an improved durability.
1) For the purpose, as a metal element wire, for example, a tungsten-rhenium (Wxe2x80x94Re) wire having a melting point of 2,300xc2x0 C. or higher is used.
2) A protective pipe of a double structure is used. That is, the protective pipe is constituted of a ceramic-made outer protective pipe and an inner protective pipe contained in the inside thereof, and the inner protective pipe is constituted of a high heat-conductive front protective pipe packed with a heat-resisting ceramic and a low heat-conductive rear protective pipe of a heat-shielding structure forming an air layer at the outside thereof.
By constructing the inner protective pipe as described above, the heat capacity of the front protective pipe can be constructed to be small by restraining the heat transfer from the front protective pipe to the rear protective pipe, and also the responsiveness can be improved by increasing the heat-receiving amount of the front protective pipe from a material to be measured such as a molten metal, etc., to increase the speed of the following up property to a temperature such as the temperature of a molten metal, etc., and as the result thereof, a thermocouple-type temperature-detecting device having a high responsiveness and a high reliability can be provided.
3) The invention has a ceramic-made outer protective pipe and a ceramic-made front protective pipe fixed to the inside of the above-described protective pipe via a 1st fixing member such that the closed head portion is projected from the outer protective pipe.
4) Also, heat-resisting ceramic-made fillers are packed in the inside if the front protective pipe and further the front protective pipe has a pair of alloy element wires each having a different composition, which are connected to each other at the above-described head portion to constitute a temperature measuring portion. Also, the end potion of an open form at the opposite side of the above-described front protective pipe to the above-described head portion is sealed by a heat-resisting glass-made sealing member.
5) Also, a hollow rear protective pipe is extended via a 2nd fixing member to the outer periphery of the above-described end portion of an open form of the front protective pipe and the rear protective pipe is disposed in the inside of the above-described outer protective pipe via an air layer (with an interval).
Also, the element wires of the thermocouple extended from the back portion of the above-described inner protective pipe are extended to the outside from the back portion of the rear protective pipe passing through the inside of the above-described rear protective pipe, and the element wires are connected to a temperature measurement apparatus and a display apparatus via compensating lead wires not shown.
A) The heat conductivity of the front protective pipe constituting the above-described inner protective pipe is constructed to be larger than the heat conductivity of the above-described rear protective pipe.
B) The above-described front protective pipe is constituted of a material made of Si3N4 as the main constituent. Also, the rear protective pipe extended to the inside of the above-described outer protective pipe is constituted of stainless steel, a material made of Si3N4 as the main constituent or as a material made of Al2O3 as the main constituent.
C) The above-described outer protective pipe has a multilayer structure made of at least two kinds of materials, and is formed in laminated layer structure formed by alternately laminating a 1st layer made of Si3N4 as the main constituent and a 2nd layer made of Si3N4 as the main constituent and containing from 10 to 40% by volume BN in a concentric circle form or a vortex form in a closely stuck state each other, and the above-described 2nd layer is formed as the outermost layer.
D) The heat-resisting ceramic, which is the filler packed in the above-described inner protective pipe, is made of Si3N4, MgO, and aluminum phosphate.
E) The above-described 1st fixing member of fixing the inner protective pipe and the outer protective pipe is constructed of ceramic fibers of SiC or Al2O3 and at least one kind of an inorganic glass selected from a ZrO2-base glass, an Al2O3-base glass, and an SiO2-base glass.
F) The above-described 2nd fixing member of fixing the front protective pipe and the rare protective pipe constituting the inner protective pipe is constituted of at least one kind of an inorganic glass selected from a ZrO2-base glass, an Al2O3-base glass, and an SiO2-base glass or at least one kind of a heat-resisting ceramic selected from Si3N4, MgO, and aluminum phosphate.
G) The above-described alloy element wires forming the thermocouple are constituted of Wxe2x80x94Re element wires so that a particularly high temperature can be measured.
Because the thermocouple-type temperature-detecting device of a high-speed responsiveness of the invention is constituted as described above, the heat received at the head portion of the above-described protective pipe having formed a temperature-measuring portion or a temperature-sensitive portion from a material to be measured such as a molten metal, etc., is hard to be transferred to the rear protective pipe and as the result thereof, the heat capacity of the front protective pipe becomes small. Therefore, the heat given by the contact of the temperature-sensitive portion with a material to be measured quickly raises the temperature of the front protective pipe to immediately follow up to the temperature of the material to be measured, whereby the temperature-measuring responsiveness can be improved.
Also, because the outer protective pipe protecting the inner protective pipe is constituted of a multilayer laminated structure using at least two kinds of materials, cracks caused by a thermal shock do not progress to the inside at a stretch but are stopped at the portion of the boundary layer between the layers of the laminated layer structure. That is, to break the protective pipe, a large breaking energy is required, whereby the life of the outer protective pipe is improved and thus the inner protective pipe can be effectively protected by the outer protective pipe.
Also, because in the invention, the outermost layer of the outer protective pipe is constituted of silicon nitride containing BN, it becomes possible to increase the contact angle formed by a molten metal to the outer surface of the outer protective pipe, a molten metal repelling phenomenon that the outer surface of the outer protective pipe repels well a molten metal occurs, whereby attaching of the molten metal to the outer surface of the outer protective pipe is prevented and the durability thereof can be improved.